Polyphenylene sulfide (“PPS”) is a high performance polymer that can withstand high thermal, chemical, and mechanical stresses. Due to its relatively slow crystallization rate, however, injection molding of parts from polyphenylene sulfide can be challenging. For example, to achieve the desired degree of crystallization, molding is generally conducted at a high mold temperature (˜130° C. or more) and for a relatively long cycle time. Unfortunately, high mold temperatures typically dictate the need for expensive and corrosive cooling mediums (e.g., oils). Attempts to address the problems noted above have generally involved the inclusion of various additives in the polymer composition to help improve its crystallization properties. To date, however, such attempts have not been fully satisfactory. In fact, the problems have become even more pronounced as various industries (e.g., electronic, automotive, etc.) are now demanding injection molded parts with very small dimensional tolerances. In these applications, the polymer must have good flow properties so that it can quickly and uniformly fill the small spaces of the mold cavity. It has been found, however, that conventional polyphenylene sulfides that manage to meet the requisite high flow requirement tend to result in a significant amount of “flash” (excess polymeric material that is forced out of the cavity at the junction of two mold surfaces) during molding, especially when high temperatures/long cycle times are employed. The production of large amounts of flash can impact product quality, and also require the costly and time consuming step of trimming the part.
Due to its relatively slow crystallization rate, however, injection molding of parts from polyphenylene sulfide can be challenging. For example, to achieve the desired degree of crystallization, molding is generally conducted at a high temperature (˜130° C. or more) and for a relatively long cycle time. Unfortunately, high mold temperatures typically dictate the need for expensive and corrosive cooling mediums (e.g., oil) in order to achieve good mechanical properties. Attempts to address the problems noted above have generally involved the inclusion of various additives in the polymer composition to help improve its crystallization properties. To date, however, such attempts have not been fully satisfactory. As such, a need exists for a suitable method for injection molding polyarylene sulfide at low temperatures while still achieving good mechanical properties.
As such, a need continues to exist for a polyarylene sulfide composition that can be more readily injection molded into parts having a variety of shapes and sizes.